1. Field of the Invention
This invention relates to a method for estimating scattered ray intensity distribution in X-ray CT from a shape of a subject and an X-ray CT apparatus.
2. Background Art
An X-ray CT apparatus detects intensity of X-rays (hereafter referred to as main ray) radiated from an X-ray bulb and going straight through a subject, and forms a cross-sectional image of the subject. At this time, detection of X-rays scattered from the subject (hereafter referred to as scattered ray) and the main ray produces a ghost image on the cross-sectional image resulting in degradation of image quality. Conventionally, the scattered ray incident from an oblique direction to a detector has been screened by placing a collimator beside the detector, but the scattered ray incident from normal to the detector has been unable to be separated. A technique simulating the scattered ray using a Monte Carlo method and removing the scattered ray component from an original signal configuring the image detected by the detector (e.g. JP-A 11-299768 (Kokai) (1999)) and a technique forming a correction data having the scattered component removed by simulation and configuring a high-precision image (e.g. JP-A 2006-334319 (Kokai)) are disclosed.
However, while a intensity distribution of the scattered ray can be estimated from a structure of the apparatus and a shape of the subject by simulating X-ray tracks by the Monte Carlo method, there has been a problem associated with taking a too long time for a purpose tracking only component incident to the detector to produce an error out of the scattered X-ray, because the Monte Carlo method tracks all scattering tracks. Therefore, application to subjects of all types of shapes has been difficult.